The present invention relates to a surface-treating agent, which is applied in the final stage of a rinsing process after formation of a phosphate film on a metal can body, diminishes a friction coefficient of interior and exterior surfaces of the metal can body, intends elevation of mobility of the can body, intends load decrease and smooth insertion of mandrel coming in and out in a coating process, and thereby prevents abrasion of the mandrel. Furthermore, the invention relates to a concentrate for treating a metal can surface, from which the surface-treating agent is prepared.
The present invention also relates to a method for treating a metal can surface, which is carried out in order to intend elevation of mobility of the can body and to intend load decrease and smooth insertion of a mandrel coming in and out in a coating process.
The metal can includes: a 2-piece type can consisting of a tube-like body part (which has a bottom) and a roof plate; and a 3-piece type can consisting of a tube-like body part (which does not have a bottom), a bottom plate, and a roof plate. A body part of these, that is, a metal can body is generally prepared by treating a metal plate in order by each process of molding, degreasing, rinsing, converting, rinsing, drying, and coating. In the processes of from molding to drying, many can bodies having been spread sideways are transferred at high speed in a wide line for treating. However, in the processes of drying and coating, the line width becomes narrow and thus, gathered can bodies are transferred one by one. In the coating process, the can bodies transferred one by one are in order printed or coated on the exterior surface.
The metal cans have been produced in large quantities as a food vessel for a refreshing drink, an alcoholic drink or the like and in recent years production of the metal cans has much increased in amount compared with other kinds of vessels. On the other hand, production of the refreshing drink, alcoholic drink and the like much varies in amount with seasons. It is general to cope with the increase and variation of the production amount of the metal cans by avoiding capital investment as much as possible in a view point of cost and by elevating production speed still more or varying it up and down. Varying the production speed up and down is very dependent upon the transferring speed of the metal cans.
As mentioned above, when the can bodies being transferred gather, they come into contact or collision with each other. Even if the can bodies being transferred at relatively slow speed come into contact or collision with each other, disadvantage to mobility does not occur.
However, if the can bodies being transferred at very fast speed come into contact or collision with each other, mobility becomes bad and their breakage or jumping out of a transfer device occurs.
Therefore, it was considered to spray a surface-treating agent to the exterior surface of a metal can body in order to diminish a static friction coefficient of the surface. For example, in Japanese Official Patent Provisional Publication No. showa 64-85292, it is disclosed that a surface-treating agent for a metal can, containing the undermentioned water-soluble organic substance, is applied to a metal can in order to diminish a static friction coefficient of its exterior surface and thereby to elevate mobility of the can. Said water-soluble organic substance is as follows: fatty acid derivatives such as an ethylene oxide-added stearic acid, an ethylene oxide-added isostearic acid and the like; alcohols such as an ethylene oxide-added oleyl ether and the like.
In the production process of a metal can, the transferring speed of can bodies is very fast and forementioned each treatment is usually carried out by spraying.
If a surface-treating agent foams when sprayed, disadvantage to maintenance of a production line occurs because foam overflows from a tank causing contamination or that idle running occurs when the foam reaches a supplying inlet coming from the tank to a spray nozzle. Therefore, it is desired that a surface-treating agent is hard to foam even if it is sprayed.
In addition, after treating, since drying is carried out by heating, it is necessary that a surface-treating agent has thermal stability at an operating temperature of the drying. If a surface-treating agent decomposes when the drying is carried out, an effect of diminishing a friction coefficient is damaged, so that jamming cannot be prevented.
However, the surface-treating agent disclosed in the forementioned publication has a high foaming property since it contains a water-soluble organic substance. In addition, the water-soluble organic substance has poor thermal stability and therefore it decomposes at a practical drying temperature, so that an effect of diminishing a friction coefficient is liable to decrease.